1. Field of the Invention
This invention relates generally to apparatus used in connection with the cultivation of bacteria and more particularly to miniaturized microbiological culture support devices and associated apparatus therefore as well as a method for using the apparatus with the devices comprising this invention.
2. Description of the Prior Art
One of the more important methods currently in use in the field of microbiology is the process for propagating organisms known as cultivation. In this process, bacteria are encouraged to grow by placing them on a suitable growth medium under environmental conditions permitting rapid replication. This process is widely utilized by practicing physicians in testing sputum and urine for the presence or absence of bacteria, for identifying the bacteria and for determining the sensitivity of bacteria to antibiotics. This process is also utilized in laboratories on a large scale for medical experimentation in order to determine the effects of various chemicals upon the growth of bacteria.
The process of cultivation of bacteria generally involves the utilization of a culture medium which is located within a culture dish. The culture medium contains all of the necessary nutrients for bacterial growth. In the prior art, a liquid medium is frequently used which has a gel consistency that is achieved by adding agar or silica gel. The culture medium is usually inoculated with the bacteria by utilizing a loop or a needle which contains the bacteria along its edge and by streaking the surface of the culture medium with the loop or needle. Frequently, a disposable cotton swab is first used for collecting the inoculum, for example from the patient's throat. The inoculum is then diluted in a diluant that is usually the same as the culture medium but without the agar. A disposable, plastic loop may then be used for inoculating the culture medium that contains the agar.
The prior art culture dish generally comprises a top or cover member and a loosely assembled bottom member having a well or receptacle portion. The bottom member contains the culture medium in the well thereof and the top overlaps the bottom member to allow an indirect flow of air into the wall during the cultivation process. Normally, the bottom and cover members are not sealed to each other so as to define individual units. The culture medium may be prepackaged in each dish and usually twelve dishes are provided in a sealed cellophane bag. Once the seal of the bag is broken the seal is open for all the dishes therein.
Before being used, the prior art dish with the culture medium therein is kept refrigerated in a sterile atmosphere to prevent contamination and bacterial growth. When it is desired to produce a culture growth, the dish is removed from its refrigerated storage and the top is removed in order to allow the loop or needle to streak the culture surface in the manner described above. The top is then quickly replaced over the bottom of the dish and the culture dish is placed in an incubator which is set at a predetermined temperature which will provide the proper growth environment. Following the incubation period, the dish is removed and uncovered and the culture medium examined to identify the various bacterial growth or colonies whose color, size and shape is characteristic for each type of bacteria.
In utilizing this process for urine culture, instead of using a loop or needle, a centrifuge tube or a syringe may be used to place the specimen on the growth medium. However, the complete process and the culture dish is generally the same as previously described.
The process of culture growth or cultivation is one of the most reliable tests for determining the presence of a specific type of bacteria. For example, growing a throat culture is a direct method for providing the physician with information concerning the specific type of bacteria present in the patient's throat. Such cultures are frequently the only way of determining whether streptococcus organisms or similar dangerous pathogens exist in the throat and whether or not antibiotics should be prescribed. More particularly, accurate identification of a specific bacteria permits the most effective antibiotic to be prescribed. Similarly, culture growth is an important means for identifying micro-organisms in a urinary tract infection.
While such tests may, in fact, be the most useful for the physician, it is uncommon that physicians will take a culture growth for each patient complaining of a sore throat or for each patient having a urinary infection. One reason is that, in order to maintain the proper equipment for culture growths, it is necessary for the physician to have a large and costly incubator, a large volume of refrigeration space, and a large supply of the loops and the culture dishes containing the culture medium. The culture dish used in the prior art practices is of relatively large size, typically about 10 cm. in diameter and about 1 cm. in depth. The medium is uniformly distributed in the prior art culture dish to a height of about 4 mm. Because of the large volume of culture medium needed to fill the dish the culture growth process involves a significant cost.
A particular drawback of the prior art structure is found in the requirement that the culture medium remains sterile. Because of the large size of the culture dishes it is inconvenient for physicians making house calls to carry along even a limited supply of the prior art culture dishes for making throat cultures or urine cultures when visiting patients.
In laboratory use, culture growth is not usually carried out on a substantially larger scale than normally employed by an individual physician. The analysis of the culture growth has, in the past been done on an individual culture dish basis by a skilled technician. The laboratory process is therefore costly and time consuming since each culture dish must be inoculated and analyzed individually. Furthermore, in laboratory use where a large quantity of culture dishes must be utilized in a single experiment, the space required for storing and incubating the culture dishes containing the growth medium becomes a problem and therefore severely limits the number of experiments utilizing this method.
While in other fields of medicine, such as immunology, the size of test equipment has been drastically reduced, miniaturization has not heretofore been achieved in microbiological culture growth. Basic problems in connection with miniaturization of the microbiological growth process are that the culture medium must remain in a sterile atmosphere prior to the inoculation and, during incubation, the culture medium must be protected from direct flow of air which may tend to cross-contaminate the culture medium with foreign organisms. On the other hand the culture medium must have an indirect flow of air after inoculation in order to achieve proper growth of the bacteria being tested. Problems relating to the safe transport of the inoculated culture medium must also be overcome.